I don't know who made the lightweight (cheap) diamond molds, but I think they are recent manufacture by injection molding. Could be done in USA or overseas (China?).

Regarding the older "clay" composition diamond mold, it started by Jack Todd, then mold was acquired by Christy & Jones.

My info comes from a very informative article by Howard Herz in the Winter 2007 club magazine. Posted in the club archives here:
http://cctn.ccgtcc.com/SampleBoxes.pdf

Look up the section on Christy & Jones (page 6 of the pdf).